Molecular Landscape in Pediatric and Young Adult Thyroid Cancer: A Brazilian Cohort Study

mutations were identified in five cases and excluded from fusion analysis. Among the samples, pathogenic point mutations were detected in 26.6% (21/79), while gene fusions were identified in 13.5% (10/74) of cases. RET rearrangements were observed in 8.6% (03/35) of evaluable tumors, including CCDC6:RET, NCOA4::RET, and TRIM24::RET fusions. Gene fusions overall were significantly more frequent in younger patients, whereas no association was found with tumor size or risk of recurrence. A high proportion of inconclusive results was observed, likely reflecting technical limitations related to the use of formalin-fixed, paraffin-embedded tissue. In conclusion, RET fusions were relatively uncommon in this Brazilian cohort but were enriched in younger patients, underscoring age-related differences in the molecular landscape of pediatric thyroid carcinoma and highlighting the need for larger, standardized multicenter studies.